Heavy Breathing on Mars?

Planetary scientists probing the martian atmosphere have found that both methane and water tend to be concentrated over the same three equatorial regions of Mars. The new find further stokes talk of life on Mars.

Researchers examining data from the European Mars Express mission first announced spotting methane in March (ScienceNOW, 24 March). At last week's International Mars Conference in Ischia, Italy, the same team, led by Vittorio Formisano of the Institute of Physics of Interplanetary Space in Rome, announced that the methane is concentrated over the same three equatorial regions--Arabia Terra, Elysium Planum, and Arcadia-Memnonia--where water vapor is concentrated in the lower atmosphere. Those are also three regions, Formisano says, where the U.S. Mars Odyssey orbiter has detected signs of water in the upper meter of martian soil, in the form of ice or hydrated minerals. The coincidence of atmospheric water, methane, and soil water "points to a common source underground," says Formisano.

The source called to mind is methane-generating bacteria that could live beneath a few kilometers of frozen crust. The accompanying water--a key prerequisite for life--supports that picture. On the other hand, the methane and water vapor could stem from an erupting volcano, a simmering hot spring, or even abiotic reactions between rock and cold ground water. But some researchers say another source may be more likely still: an exotic mix of methane trapped molecule by molecule in crystalline cages of water ice. On Earth, such methane hydrate--which is found beneath the deep seabed and within permafrost--usually comes from bacteria decomposing organic matter; on Mars, either life or chemical water-rock reactions could be responsible.

The methane-water coincidence "is a real neat observation," even if "it doesn't uniquely point to life," says Stephen Clifford of the Lunar and Planetary Institute in Houston, Texas. Details have yet to be published, leaving open the possibility that a small part of water vapor's spectral signature has been mistaken for a spectral line of methane. And planetary scientists find it curious that any regional concentration can be recognized at all, because martian weather mixes methane around the planet in a matter of months. Things may get clearer in the next couple of months as new data as well as telescopic observations come out.